Treatment of Vomiting and Gut Disorders Flashcards
Where is vomiting controlled neurally?
2 units in the medulla:
- vomiting (emetic) centre
- chemoreceptor trigger zone
Describe the location and function of the vomiting centre
- found mainly in medullary and pontile reticular formation extending into spinal cord
- receives nerve impulses from both vagal and sympathetic nerve fibres
- responds to incoming signals to coordinate emesis
Describe the location and function of the chemoreceptor trigger zone
- in area postrema in floor of 4th ventricle
- sensitive to chemical stimuli and is main site of action of drugs that stimulate vomiting
- also involved in mediation of motion sickness
What things trigger nausea/vomiting?
- stimulation of sensory nerve endings in stomach and duodenum
- stimulation of vagal sensory endings in pharynx
- drugs or endogenous emetic substances
- disturbances of vestibular apparatus
- various stimuli of sensory nerves of heart and viscera
- rise in intra-cranial pressure
- nauseating smells, repulsive sights, emotional factors
- endocrine factors
- migraine
Describe the stages of vomiting
- nausea: feeling of want to vomit. associated with autonomic effects such as salivation, pallor, sweating
- retching: strong involuntary effort to vomit but unproductive
- vomiting: expulsion of gastric contents through mouth
What are the types of vomiting?
- projectile vomiting: suggests gastric outlet or upper GI obstruction
- haematemesis: vomiting fresh or altered blood
- early-morning: pregnancy/alcohol/metabolic cause
Why are anti-emetic drugs given?
- to stop nausea/vomiting
- only prescribed when cause is known
- treat cause where possible
- if indicated drug is picked according to aetiology of vomiting
What are some example indications for anti-emetics?
- severe vomiting during pregnancy
- post-operative nausea and vomiting
- motion sickness
- other vestibular disorders
- induced by cytotoxic chemo
- palliative care
- associated with migraine
List the types of anti-emetics?
- antihistamines
- antimuscarines
- dopamine antagonists
- 5HT3 antagonists
- neurokinin 1 receptor antagonists
- synthetic cannabinoids
- steroids
- other neuroleptics
What are antihistamines, their use and side effects?
- HI histamine receptor antagonists
- uses include motion sickness and vestibular disorders
- side effects vary and include drowsiness and anti-muscarinic effects (eg. dry mouth)
What are some examples of antihistamines and their uses?
- cinnarizine (motion sickness/vestibular disorders)
- cyclizine (motion sickness)
- promethazine (severe morning sickness)
What are antimuscarinics and their side effects?
- muscarinic receptor antagonists
- lock muscarinic receptor-mediated impulses from the labyrinth and from visceral afferents
- side effects include constipation, transient bradycardia and dry mouth
What is an examples of an antimuscarinic and what its used for?
- hyoscine hydrobromide used in motion sickness
What are dopamine antagonists?
- dopamine D2 receptor antagonists
- act centrally as dopamine antagonists on CTZ
- active against CTZ-triggered vomiting but not stomach induced vomiting
What are examples of dopamine antagonists?
- phenothiazines (neuropletics/antipsychotics)
- chloropromazine
- prochloroperazine
- domperidone
- metoclopramide
What are 5HT3 antagonists and an example
- blockers of 5HT3 receptors in GIT and CNS
- very useful for patients experiencing nausea/vomiting post operatively or on cytotoxic therapy
- eg. ondansetron
What are neurokinin 1 receptors and an example
- an adjunct to dexamethasone and a 5HT3 antagonist in preventing nausea/vomiting associated with chemo
- eg. aprepitant
What are the synthetic cannabinnoids, the side effects? and an example?
- CB1 receptors
- used for chemo patients unresponsive to conventional anti-emetics
- can cause drowsiness
- nabilone
What are the types of laxatives and examples?
- bulk-forming (ispaghula husk)
- stimulant (senna)
- faecal softeners (docusate)
- osmotic laxatives (lactulose)
- peripheral opiod-receptor antagonists (methylnaltrexone bromide)
How does diarrhoea affect the GIT?
- increases motility
- decreases absorption of fluid and electrolyes
How would you approach treating acute diarrhoea?
- maintain fluid electrolyte balance (oral rehydration prep)
- antimotility drugs
- antispasmodics to reduce smooth muscle tone (eg. hyoscine butylbromide)
- occasionally anti-bacterial agent used
What is used to treat chronic diarrhoea with examples?
- anti-motility agents (loperamide)
- absorbents (kaolin)
- bulk forming drugs (ispaghula)
What is contained in bile?
- bile salts
- bilirubin
- cholesterol
- lecithin
- plasma electrolytes
What medicine can be given to treat gallstones?
- ursodeoxycholic acid to dissolve the stoned
- if mild symptoms
How is biliary colic treated?
- with opiods such as morphine as it is very painfully
- if vomiting given parenterally or rectally
- if pain continuous over 24hrs then hospital admission
How does colestyramine work and what is it used for?
- forms insoluble complex with bile acids in intestines
- relieves itching associated with partially biliary obstruction and primary biliary cirrhosis
